Wrangling over Brexit obscured the more important question, whether the UK and the EU member states within Nato agree with America’s new view of the world. Many European politicians view Trump himself as the key challenge for the West and hope that he is simply an aberration in US politics. There have long been disagreements on significant matters of foreign policy, such as how to handle Russia, the nature of military intervention, and the Iranian nuclear deal. Previously these have been papered over by the primacy of the “War on Terror”. Even that project has come under considerable strain with operations in Syria exacerbating a number of political fissures, not least with Turkey. Unlike previous transatlantic disagreements a much more fundamental split about the nature of the world is emerging.

As a result there is reason to question whether EU countries will fall into line with US strategy. If they do not, the ramifications for Nato are serious. Most European Nato members face a domestic terror threat not replicated in the continental USA. Furthermore, China remains only of peripheral geographic interest, unless a south-east Asian conflict results in America triggering Nato’s Article V. For instance, would EU members of Nato really want to support a bellicose American president in Korea?

Equally, would America come to the aid of Turkey or one of the Baltic States if they invoked Article V? Russia, which is implicitly seen as a secondary threat to China in the US, is a more direct threat in Europe. Nonetheless, it remains a divisive issue within the EU. It is plausible that an operational bifurcation might emerge within Nato, with the US focusing on countering China, and the EU concentrating on Russia. This could cement a division of labour that eventually results in a split.

This isn’t just a question of diverging interests and values. Hidden in Mattis’s NDS was a far more important acknowledgement of changing material circumstances that has largely been ignored. He wrote: “For decades the United States has enjoyed uncontested or dominant superiority in every operating domain. We could generally deploy our forces when we wanted, assemble them where we wanted, and operate how we wanted. Today, every domain is contested — air, land, sea, space, and cyberspace.” In three sentences he acknowledged that the US can no longer rely on unassailable hegemonic power. Clearly this will have important consequences for America and her allies in the practical exercise of military power. The great unknown is whether this decline in US power is permanent, a slow drift to a state system that would have been familiar to the titans of early 19th-century statecraft, Metternich and Castlereagh. Certainly, the NDS is prioritising preparation for future great power conflicts at the expense of fighting today’s war against non-state actors such as IS.

Since the Clinton administration, successive secretaries of defence tried, unsuccessfully, to move away from the so-called “two-war strategy”, the ability to fight two wars concurrently. In addition to the crippling cost, many argued that the so-called Third Offset Strategy would allow vastly superior technology to defeat enemy forces. In 2012 Obama reduced the strategic posture to “defeat and deny”. This meant defeating an enemy in one territory, while simultaneously denying another territory to an aggressor. The NDS has created a paradox. Whilst stating that the US faces two distinct challenges from China and Russia, and a variety of smaller regional threats, actual capability will be cut back even further to “defeating aggression by a major power; deterring opportunistic aggression elsewhere and disrupting imminent terrorist and WMD threats”.